Heat the 2 cups water to boiling, add cauliflower and onion. Cook until soft, approximately 10 minutes. Do not drain. Blend with an immersion blender or in a regular blender until smooth.
Heat butter in a three quart saucepan until bubbly, add flour, salts and pepper, cook and stir for one minute. Remove from heat, stir in the last cup of water and the bouillon, return to stove, heat to boiling, stirring constantly for one minute. Add cauliflower mixture, heat to just boiling, slowly add 1/2 and 1/2. Heat just until hot.
Sprinkle each bowl with a touch of nutmeg, optional.